Process of suspension polymerization of vinyl halide utilizing gelatin as dispersingagent



specific means.

2,833,754 PROCESS- OF- SUSPENSIDN POLYMERIZATION or HALIDE {UTILIZING 'GELATIN' AS msrnnsnuo AGENT 6 Claims. (Cli'260-92.8).

This invention relates to the production of synthetic resins,.and is more particularly concerned with theproduction of resins comprising polyvinyl chloride.

The invention is concerned primarily with improvements in what is known: as granular polymerization. Granular polymerization is-known also as: pearl polymerization' and suspension polymerization, the three terms being: synonymous. More particularly, the invention is concerned with the production of high-quality, general-purpose, polymeric material by the granular polymerization method, such that the stock material so produced may be employed, inthe vast majorityof cases, for whatever purpose and in whatever manner maybe desired. Those skilled in the art' will recognize. the ambitiousnessof the undertaking because of the multiplicity oficharacteristics that are necessary in order for a stock material to be so generally acceptable. Althoughthe invention is not restricted to the polymerization ofasingle monomeric material, for purposes oi simplicity, the description oftheinven'tion is centered upon the productionof polyvinyl chloride, the properties thereof that characterize high-quality, generalrpurpose stock material, problems that have been encountered in the past in. itsproduction, and the improvements wrought by thisinvention whereby. those problems are overcome.

The general procedure that: is followed incarryingout polymerization reactions according to the granular polymerization method is now well-known to.involve the suspension. of the monomer in water and, wh'de suspended, etfecting polymerization. Heat and catalysts are employed as polymerization aidsandthe suspension-is maintained during the course ofthe-reaction bystabilizing the system with one or more of a, number oi materials known as suspension stabilizers, for example, methyl cellulose, polyvinyl alcohoLsodium alginates, gumtragacanth, and the like. When. the polymerization reaction is complete, in well-handled processes, a goodly portion of the polymer may be recovered inparticle'or, granular form by filtration or centrifugation without the aid of any additional The product is thereafter washed and dried, after which it is ready for market. This type ofprocess has several outstanding advantages over the process of polymerizing which is known as emulsion polymerization.

Emulsion polymerization conducted in a. system in which the monomeric material is, dispersed in water by means of a surface-active agent to form. an emulsion. Polymerization is, carried out with the aid of heat and a water-soluble catalyst. This procedure differs from suspension polymerization in many respects, not the least important of whichyis the use of a water-soluble catalyst. Normally, suspension polymerization employs only oilsoluble catalysts.

At the, conclusion ofthe emulsion polymerization, the

polymerization, product remains dispersed in the system as a finely-divided mass that is referred to as a latex, In order, to. recover the. product, it is, necessary to efiect coagulation of the latex whereby the emulsion system is United States Patent broken andthe polymer is precipitated. This may be accomplished by adding anelectrolyte to the latex but such addition of electrolyte is usually undesirable for reasons to be stated. Accordingly, mechanical means may be resorted to in order to break the emulsion. However, even if mechanical means are used to break the emulsiomthe residual electrolyte from both the catalyst and theemul-' sifying agents is still associated with the precipitatedpolyrner.

The precipitate is extremely difficult to wash free of electrolytes whether present for polymerization or coagulation purposes. Hence, the final product usuallycon.- tains impurities which render it quite inferior for a number ofits important uses. In particular,,.it is almostimpossible to prepare a material of good clarity such as is most desirable for use in preparing films and sheets'.- Secondly, where the product is to be employed incer-, tain. electrical applications, its dielectric properties are severely impaired even where great care is employed inwashing the product. The objectionable materials-cam not be removed to the necessary extent without applying lengthy washing procedure; Depending upon, the degree of impurities present, strength properties of the product may be impaired. Because of the difi'iculty of washing the precipitate, emulsion polymerization is costlyand it is primarily because of this and the above-noted=disadvan'- tage that attention in recent years has been directed to a greater degree toward the granular polymerization-method. This latter method, asindicated above, when managed properly, results in the format-ion of a granular mass that maybe washed free of impurities with ease and quite simply dried.

There are many variations of. the granular-polymeriza tionmethod generaly described above. These variations appear in the art because of specific difficulties that areencountercd in its. practice. The simple change from emulsion polymerization. to granular polymerization does not leadv to problem-free operation. In fact, some ofthe difiiculties that are encountered in emulsion polymerization. are encountered also in granular polymerization, notably, the production of a stock material which, when processed to form products, contain. what is known to. the art. as fisheyes. In the. production of a-high-quality, general-purpose polymeric material, it is perhaps misdescriptive to refer to any particular disadvantage as being most important. However, if any single one ismost important, the disadvantage offisheye formationisait. This is because of the .fact that all products formed firomfisheye-producing polymeric stock are inferior in quality in several important functional aspects, dependingsupon the number and size of fisheyes present.

Fisheyes may be visualized as small. blotches, actually having the appearance of the eyes. of a fish, in the final. plasticized polymeric product. They are believedv to .resuit from the failure of some of the individual particles. ofthe polymer stock to associate with the plasticizers Thus, as to. substance, they are merely small particles. of. unplasticized polymer surrounded by relatively large seas of plasticized polymer. Since the plasticized material isint'ended to be homogeneous, fisheyes indicate poor homo geneity'and are imperfections in, the. final product; .A relatively small number of, fisheyes can. be toleratedin. the finalproduct; in fact, it appears .i mpossibleto" elimi nate themcompletely by any process. The seriousness. of their presence in large. numbers may be indicated flby the'follbwingcomments which refer to the undesirable.

" they are not clear and transparent; instead, they present other reasons which need not be mentioned in view of the ones above noted.

The problem of fisheyes can hardly be over-emphasized. Their presence has been studied extensively by most highly skilled artisans who recognize them as being the most serious single problem in the production of high-quality polyvinyl chloride products. As will appear from the discussion hereinafter of the present invention, the premise suggested above provides a reasonably valid point of departure from which their presence may be understood and controlled.

While, as noted above, the polymeric mass that is produced by .a properly managed granular polymerization method may be quite easily and quickly washed free of impurities and is easily dried, it is extremely difficult to control the particle size of the granular mass that is formed, whereby suchease of washing and drying is attained.

From the standpoint of operating efficiency, and thus the commercial advantage in low costs that the granular polymerization process affords, the problem of obtaining uniform particle size is equally as serious as the problem of fisheyes. In the first place, it will be recalled from the foregoing paragraphs that the polymerized product must be separated from the aqueous medium. This may be accomplished by usual filtration or centrifuging methods provided that the product is within a suitable particle size range. If the particle size is too small, separation will be diflicult and extremely slow and, in fact, may be impossible in the practical sense. A mass of small particles holds the occluded suspending medium and prevents its release from the mass. Also, the particles themselves may pass through the filter along with the liquid. On the other hand, if the particle size is too large or if the particles are not of a uniform desired size, serious obstacles are encountered in processing the polymer to its final product stage. Because of the processing requirement for handling larger particles, an inferior product results.

Various attempts'have been made to explain the reason for the formation of large globules or agglomerates of the polymer. It has been reported that during the polymerization reaction, the mass passes through a sticky, tacky state which isnot broken up completely in the succeeding phase of the reaction and that violent agitation only seems to increase the tendency toward agglomeration. Also, it is reported that the reaction rate and the temperature in the reaction zone is thought to be responsible for the problem. These possibilities need not be denied here as they may be entirely valid assumptions when considered in the light of the particular process in which they originate. However, it is suggested herein that the proper approach to solving the problem of uniform particle size resides in the basic suspension system itself, and that, if the suspension system is proper, a preferred particle size can be obtained, and other conditions, such as temperature, reaction rate and agitation stand reduced in power of influence upon particle size.

It may be said in respect er such other explanations and the mentioned conditions that unquestionably there appear to be optimum reaction rates, temperature limits and conditions of agitation which desirably should be correlated with a basic suspension system and such are indicated hereinafter in connection with the process of this invention. It should be noted that among the most important properties generally regarded as requisite in highquality, general-purpose polyvinyl chloride are dielectric properties, heat stability, plasticizer compatibility under processing conditions, high strength properties, clarity and color, high bulk density, and processability. As noted above in part, these properties, for the most part, are either attained or fallen short of, depending upon the control of fisheyes and particle size and, further, as noted above, these two conditions depend in turn upon the operating techniques that are employed in the granular polymerization process.

It has now been determined that despite the variety of environmental conditions afiecting the polymerization reaction, an excellent control of particle size distribution in the resultant polymer can be efiected by the practice of this invention. Before describing the present process in detail, it will aid in an understanding of the invention to point out that the discovery has been made that the final particle size distribution is largely determined during the formation of the initial monomer-water suspension. It has further been observed in many instances that the most stable suspension possible is obtained by establishing the desired particle size at a pH greater than the isoelectric point of the dispersing agent employed. As used in the specification and claims, the expression isoelectric point is intended to mean the point of electric neutrality or zero potential, hence, the pH value at which a substance is neutral.

While iris advantageous to form a monomer-water suspension at a relatively high pH in order to insure as stable a dispersion as possible, effecting polymerization at such a high pH has been found to be disadvantageous in many instances. Contrariwise, polymeric products having excellent colloidability and particle porosity are obtained by polymerization at a pH lower than the isoelectric point of the dispersing agent. However, a low pH generally tends to reduce the suspending action of the dispersing agent. Accordingly, if a high pH value is employed throughout the formation of a monomer-water suspension and subsequent polymerization, which procedure would insure a stable suspension, other desirable polymer properties are impaired. On the other hand, if the entire procedure is carried out at a low pH in order to obtain proper colloidability and particle porosity, accurate control of polymer particle size distribution is a difficult problem.

It is, therefore, a principal object of this invention to avoid the foregoing difiiculties and to provide a polymerization process which permits not only excellent polymer particle size control but also provides excellent colloidability and particle porosity.

A further object is to provide a new and improved polymerization process for the manufacture of polymers having a predetermined particle size distribution.

These and other objects and advantages of this invention will appear more fully from the following description.

The process of this invention comprises carrying out a polymerization reaction from an initial monomer-water suspension which is established with the aid of dispersing agent under conditions which permit the formation of the most stable dispersion possible, and thereafter polymerizing the thus-dispersed monomeric material under different conditions with the aid of heat and a catalyst.

The practice of the present invention is particularly advantageous in systems employing amphoteric dispersing agents such as gelatin. In such systems, it is a feature of the invention first to form a monomer-water disless than the isoelectric point. In many instances, it will be understood, of course, that the initial stable monomer dispersion can be effected at the unadjusted or ambient pH value of the monomer-water mixture so long as this pH is greater than the isoelectric value of the dispersing agent employed. At times, depending on the particular the desired stable suspension, by'addition of basic materials to insure that the isoelectric point of the suspending agent is exceeded.

Numerous attempts have been made by highly skilled chemiststo polymerize vinyl chloride with the aid of gelatin as a suspension stabilizer, whereby a product, such as is sought herein, may be produced. According to recurring indications in the literature, it seems to be wellestablished that conventional systems including gelatin as the sole suspension aid fall far short of what is required in the industry and that serious problems attend its use. It was reported very early in the literature that gelatin is a suitable suspension stabilizer. However, experimental operations in accordance with the broad early teachings serve only to reveal the serious difiiculties described above. According to this invention, it has been discovered in the very face, so to speak, of the ditficulties of the sundry prior teachings thata high-quality, general-purpose product, notably, polyvinyl chloride, can be produced, typically employing a small controlled quantity of'gelatin as a suspension stabilizer, by" establishing a stable monomer-water suspension under ambient pH conditions, i. e., at a-pH greater than the pH of the isoelectric point of the gelatin in the case of alkali-hydrolyzed gelatin, and thereafter reducing the pH and effecting polymerization while maintaining the pH in the system throughout the polymerization below or on the acid side of the isoelectric pointof the gelatin. Such a procedure utilizes the gelatin at a preferred pH to produce a stable dispersion of monomer;and thereafter accomplishes polymerization at a lowered pH under conditions which impart both excellent colloidability and particle porosity to the resultant polymerio'productj Q Q Gelatin is known to be an exceedingly complexproteinaceous substance which is derived from animal substan'ceby various processes. The material is commercially available-in three slightly differentforms, 'all of which are useful in the-practiceof this invention. These forms are a so-called acid hydrolyzed product', 'a so-called alkali, i.'e., lime,"hydrolyzedgproduct, and a non-ionized form obtained'by'hot fwater hydrolysis of animal substance. These materials, as supplied commercially, vary slightly in their isoelectricpHs, namely from about 7* to"8.2 for the acid'produc't, about 4.8 to 5 for the alkali product, and about 4.7 for the non-ionized form While the present invention may be practicediemploying any of these three forms of gelatin, the alkali hydrolyzed material has been found'tohave excellent usefulness. Accordingly, it is a feature of this invention'to conduct the polymerization, employingalkali hydrolyzed gelatin as a dispersing agent, by first establishing a stable suspension of monomer in water with the aidof the gelatin at am in excess of its isoelectricppoint,thereafterreducing the pH of the system by addition of an acid,*such' as phosphoric acid, or otherwise, t'oa pH less thanthe isoele'ctricpoint of the'gelatin, and effecting polymerization withrthe aid of heat and a' catalyst. In practice, excellent re'sult'sLare obtained by establishing a stable suspension 0f monomerin water ata' pH greater than about 15.0 to36.'8 and subsequently lowering the pH to a valueof about2 and 5, particularly between 2.5 and 4, andeflectingpolymerization while maintaining a pH within this range em-' ployingl-heat, a catalyst, andcontinuous agitation during the polymerization. It appears that when employingan alkali hydrolyzed gelatin, superior results are-obtained when the pH during polymerization is maintained ata value withinthe range of from about 2.7 to 3.2, which,

of course, issubstantially below the isoelectric point of the-alkali hydrolyzed gelatin. h p "--In' addition, it'has been found that the "ultimatelyobthemreadily worked with a plasticizer and the like and, moreover,- particles having high porosity, which of course is' desirable from the standpoint of acceptance of the plasticizerQ It is apparent from the extended experimenta-' tion leading to the present invention that the phenomenon obtained by conducting the polymerization employing gelatin as a suspending agent, and'at ap'H below the isoelectric point=of the" gelatin, is largely responsible for the advantageous results obtained,'-particularly with respect to the production'of fisheyes, when the reaction is carried out in accordance with the preferred*'conditions hereof are minimum in number and relatively small in size; i

" In carrying out the method of this invention, theobtem tion of a stable monomer-water suspension and subsequent lowering of the pH before effecting polymerization is most conveniently accomplished by forming a stable monomer-water suspension under ambient pH conditions above the isoelec-tric point of the dispersing agent, thereafter continuing agitation for a predetermined period of time until the desired particle size is determined, subse quently introducing a small amount of acid to lower the pH below the isoelectric point of the gelatin orother amphoteric dispersing agent, and then efiecting polymerization with the aid of heat and a catalyst.

i In practice; the specific time interval in which a stable monomer-water suspension is established before addition of acid or other material capable of lowering the pH is dictated by the particular polymerization system. However, it'has been found in the polymerization of vinyl chloride, using gelatin as a suspending agent, that it is advantageous to add vinyl chloride monomer and gelatin to Water and agitate for a period ranging from a few minutes, e. g 5 minutes, to one hour or more before adding catalyst and acid. At present, it is preferred to delay the addition of acid for about'30 niinutes after agitation of the water-monomer mixture is begun. In large-scale applications, it will be understood that a more extended delay generally is desirable in order to permit the monomer-water dispersion t0 reach'the' desired reaction temperature'before lowering the'pH; Hence, in

- such'a'pplications, periods of delay of up to one hour or tained product comprises particles off'a size rendering. 15'

more after the desiredr'eaction is reached are typical.

The resultant polymer exhibits an improved particle size range while also having excellent colloidability' and par ticle porosity. Within limits, it has been foundthatpoly;

rner'particle size distribution is generally proportional'to the period of'delay, i: e.,the longerthe period of delay before the pHis lowered below the isoelectric point of the gelatin, the sheaths particle size. Moreover, the

process of the present invention is not merely a means of providing an e'xtremely fine particle size, but it will be understood that it permits the production of a polymer having a desired particle size range." As pointed outhere inbefore, the-obten'tionof asproduct characterized by a relatively narrow particle size distribution' withina de sired range is far more advantageous thanmerely providing an extremely fine particle size product comprising only a comparatively small fraction of the total .polynierpro e al- 7,1 4 v J'J Refer'enc'ehereinto gelatinis for convenienc'eand the term as employed denotes the'several forms. I Such refer encejisnot intended to exclude. from the scope of'this invention the'use;'ofjo'thersnsp'endiiig agents in combination' withgelatimiiincluding various materials such. as methyl ieellulos'e, polyvinyl alcohol, 'guin tragacanth, sodiuin alg'inatesgand the like; Gelatin may suitablybe added to thesystem'in quantity of from about Q.l00.45 percent" byfweightfof the vinyl chloride monomer and excellent'resultsare obtained in all respects within this range, and especially so if the pH of the system, in the case of the alkali-hydrolyzed material, is reduced to about 2.5-3.5. For example, atpH 2.8, results which are about equally good are obtained by using eitherabout 0.l00.15 percent or about 0.40 0745 percent gelatin.'- However, at

bet r: esul is .hh i i sl h ldts hi th st nts. PH and w th sels iii. consultations-qt r about -25- 213; Pe cent y wei ht o ,r as t this; l t e perssn ase t sela in s P efer e Numero smh nar.

tlollfilflfiltl lk and pH m yb qmplc t wi hin he-t pes u es d eireint te sh. but ssts q ed'es t lna isi eneststobe p im inile. the. n ee s y wh c poly iny shl ride esins home s. all. WEE

may he nteraredaeset i s to h s veiiti n n o es he.

corr i et a u an a number eac ion on itions. henro s in the main, is no ditlie l ternsnage as i su tained eemmere alep ti nl ishesesssty iily' o V observe with care the various conditions that are described her in wh teb titis l v d, a Pro uct s obt in d; which i equ l. to. t not sup r or o. any kn wn co me al mlwinylehlet e ptesl ie l v iTh aet ont m s n t inqrclina ely lensl t re u rin less than, about hours under preferred conditions and, ittl s ed, the. rea tion an be spe sd: up o si erably In order; that those interested in preparing resinous mate: rials in -accordance with this invention may do so with facilityyit is desircdlq make spccific'reference to the sew H eral variables which are involved, and, further, to call attention to certain precautions. that have, been found to contribute, at least in asmall way,lto the overall success of the process. It will be appreciatedthat theconditions hercinaiter referred to may be varied from a, sugge nt i m fis c th r becau thesu ce s of the process does, not depend uponflthemaintenance. of the.

condition with. such exactness, or because the alteration of a particular condition, may be. compensated for by theand the invention is not limited to the application of such.

precautions, their observance is recommended, especially in the production of polyvinyl chloride whereby, in some cases, a better product is produced or a particular difliculty is reduced in its magnitude.

] A i wi a sh p m i zs e f e s i i tent- Pe ature ge era y results in t e produ o a mat rial of, reduced strength and, therefore, thetemperatnre should be maintained at a level consistentwith good molecular weight and adequate speed of the reaction. For example,

lauroyl peroxide is an effective "catalyst in the polymers 8 etrths l r il wn' polymeri atio at lysts with. s a es: ttatieas st 94 70-4 n r ht by we h of the tn q n t Hq e etrqs sl t es i n r ns b ut Q- i Q fi l enter mo sui a hee i s impro eac ion. tars wand; genet l y, about 0- 2 P n hyw isht et mss m n efer e While the t e o ss es i e.

catalyst concentration are not especially notable, it has been observedthat an excess tends to produce a material it it esl he t b ity, n ne s e ht y educed strength characteristics .which'are apparently due to. a reduction in molecular weight. 7 In selecting the catalyst, especially if the end product is to be used in electrical applications where dielectric strength is a factor, care should be taken to select a catalyst which will not be detrimental in this respect and, further, it should not exert an cmulsifying ellect The peroxide catalysts are Pr femedl su sy pe x s a u t b e d snesial y t es e, c talys -:7

As ll 1. w he. shdersts l h ethod y h h Po y merization is accomplished in the practice of this invert; t es i iy lyes a cr tica eq e f process sever, before discussing these steps in detail and illustrating their use, by example, it will be understood that no particular sequence of initial dispersion of reactants is esess ryl alth u h t is e ed p b e o a d B99 5? met and. d p s agen to water at an l at d tells: pers sts. st .5-5? om ha shove am i n ent: nets ute. and then. ith u f ent a i a o to e .t see l dfnersi It. is feature st th' .Y ttien that h s in ia disp tsien. be ac p hed t s p i xce s Qtthe. isoel ie Point f h p sing a e t employed. th shy to P rmit totms of a t o ghl st b di P-e this o m n me in he wstsh h. a dis ts ht has heen; f un ng l y l te o h bl l lq l st acontrollable particle size distribution in the polynlerie material. After an initial stable dispersion is obtained, the present invention, of course, contemplates lowering the H oi th d s e s y t m o a value e han the pH' he i se ee ie point f h m q e e d snei itis iZation of vinyl chloride and excellent results arethereby obtained by operating at a temperature of about 13,0 F. Thistemperature range isinmost instances pref tenjed. Howvci'tf -hc r e'action proceedswith good order! at tron n about, l05,?-.l60, F.,falthongh aboutllj .+:l 40

F is" moresuitrblej since at about 10.5 f F. thereaetion iss owrahd. a t per e o out F- nd above W ne nde r ble fus o p r cl maytslseplace- M l The invention is not restricted toany particular eatas.

lyst, since the reaction conditions sug ested doifnot'intcrs tere with. the activity of. the catalyst and 'no W lls recogniu gd catalyst is.known whichd efeats the ends of the invention. Accordinglyi there maybe employed, tor

example, any of the i well-knownlcat' alysts, such hen wy p ox de. a yl; P o ide," idi nr y moan. acetyl benzoyl peroxide, diacetyl peroxide, p-te rtiarybutyl perbenzoate, tertiary butyl perlaurate, dietertiary, h y Pe de; o gan c az mpou ds, lu 1 s pha alphaGaZddiisobutyronitrile and dimethyl alph alpha azn ii butyrate are suitable Ea h c talys s i hav p mum c n n ration. that to 54?:13 concentration sufficient to eifect a substantially. complete polymerization a a s itab e rea tion, irat r ac ion P oceeds wit u slitll lty .e .di saqvau aseinlth pre e ce o ag nt employed n ef t P m i n w i e ins ntaining such a pH. The polymerization preferably is con-., ductedwith the aid of a catalyst and heating, together ths htiii ipiis ssitation- Th r ittie m y be r ed i i tl edpeteeh c n ersion o suh s t y e if e d, ut may a so he. term nate h t of c m let on fl hed as. son: yen ehee of Plant eq d e s may c e e- W eitthe tesetion. issem le tosthe de re x en th po y er may, he; sstlai edrom he remaining. mo e and ts et nme l imzhy hqwn mea s I r Raw mate a p i Qt nd sent f t e a e. q i sis: nificant, since important properties of the product may he, adve se y-attested h I3 p c l aldehy e lehe i l ta et le ii compounds, irq and odium s lts, e le mss t fat seid an he lik my be i he imm te ia or e es he ste r m. an u ide. s urc and h sst l s h l l take to nsur reasona le tq ur y stalltim s- Vari us ae tls may h u il zed to st the esi ed pH value, the prominent controlling factor in its selection being that it should not impair dielectric properties. Thus, acids such as. sulfuric, hydrochloric, phosphoric, citric, oxalic, and acetic are suitable, phosphoric acid being preferred, e i

- [Theiwater-monorner ratio in the system is not critical. This ratio may vary from about 1.75-4z1. More suitable; however, due to decrease in volume to be handled, is sw e -momma ratio ofabout 1,90-3 :l, the preferredra'tio being about 1.90-:-2. 2S:1. All of these ratios re ysl mej et s I n sti that h se's i let i he a m he tet i l s stand'the invention and a method by which the may he carri d i ts heet; he el s speci c e i 2l sh 9fis t v 0.250% (by weight of the monomer) of lauroyl peroxide,

about-0.300% (byweight of the monomer) of alkali hydrolyzed acid.

- I 'Proceaure About 31 gallons of deaerated watera r e charged to. a

glass-lined jacketed reactor, the water being at room tem perature. A vacuum of about 27 inches of mrcury' is pulled on the reactor and vinylchloride monomer introduced to the reactor to. bringit back. to atmospheric pressure. The vacuum treatment is repeated and more vinyl chloride monomer is introduced to the reactor. Gelatin di'ssolvedgm a small amount of deaerated water is added and agitation eifected for 30 minutes, after which the catalyst is introduced and dispersed for minutes The monomer is then charged and a stable dispersion formed at a pH above the isoelectric point of the gelatin by agitation for 30 minutes. Phosphoric acid is then added and dispersed by agitation to lower the pH of the system to a value below the isoelectric point of the gelatin.

All valves are then closed, the agitator adjusted to turn at about 250 R. P. M., and the reactor is brought to about 125 F. over about the next two hours and there maintained until the reaction is complete. The system is, of course, under pressure at this point and the pressure remains constant until the reaction is at about 80 percent conversion, at which point a sharp and distinct pressure drop occurs of about 2 to 5 pounds. When this pressure drop occurs, cold water is delivered to the jacket and the system is cooled rapidly to about room temperature. The charge is then blown to a centrifuge and there spun as dry as possible, after which it is washed with about four displacements of water. The mass is then again spun dry, after which it is delivered to trays for final drying. It is then a finished material, ready for processing.

EXAMPLE II Formulation The following quantities of materials are employed: 33 gallons of deionized deaerated water, 16.7 gallons of purified vinyl chloride monomer, 0.25% (by weight of monomer) of lauroyl peroxide, 0.3% (by weight of monomer) of alkali hydrolyzed gelatin, and about 20 mls. of 36% HCl.

Procedure The procedure described in Example I is followed in this example and a product comparable in substantially all respects is obtained.

EXAMPLE III Formulation The formulation in this example is comparable to that of Example 11, except that 20 mls. of 95% acetic acid are substituted for the hydrochloric acid of Example II.

Procedure The procedure of Example I is followed and a productanalysis of the product of the method of this invention is as follows:

gelatin, and about 20 mls. of 85% phosphoric -10 Screen: Percentia On 20 mesh On 40 mesh 2' On 60 mesh--- '3 0n.80 mesh v On l00mesh 3 On 200 mesh 45 Thl'tl ZOO mCSh 45 Those skilled in ,the art will recognize that this size range provides excellent uniformity of particle size well within the limits permissible by processing methods. Ac: cordingly, the products formed from the polymer are'entirely free of the disadvantages mentioned hereinbefore relating to problems that are encountered because of excessive quantities of particles th'at are too large or too small.

The polymer has excellent dry-blending qualities. For example, it may be mixed with any ofthe well-known plasticizers, both monomeric and polymeric types, without any tendency to become sticky or syrupy. Examplesof such plasticizers are dioctyl phthalate and the polyesters formed by condensation of polyhydric alcohols and dibasic acids, as well as expoxidizedunsaiturated polyesters;

'Products which are formed from granular polymeric material produced as in the above example exhibit outstanding properties in all respects. Because of the substantial absence of large fisheyes and the very small quantity of small fisheyes, sheets, films, and other finished products are unusually strong. Likewise, such products are of excellent clarity.

In the practice of this invention on a commercial scale it will be realized, of course, that a certain amount of time is consumed in heating the monomer-water-dispersant mixture to the desired polymerization temperature. A typical time is one hour and 15 minutes, during which time agitation is continued. The following data indicate the polymerized polyvinyl chloride particle size distribution obtained using 0.3% gelatin by weight of monomer as a dispersant and by varying the periods of delay after the desired polymerization temperature is reached before adding phosphoric acid to produce the system pH.

Particle Size Distribution, Period Mesh Bulk Run Time (Hrs.) of Density, Delay Gms./cc.

(Hrs) 60 100 200 200 As shown by the above data, a finer particle size distribution is obtained by a longer period of delay in reducing the system pH below the isoelectric point.

While the invention has been described with particular reference to the production of polyvinyl chloride, it may be employed also in the production of polyvinyl chloride copolymers, especially icopolymers in which vinyl chloride constitutes at least of the mixture of monomeric materials. Thus, the process of the invention is applicable to processes wherein vinyl chloride is polymerized with other unsaturated monomeric material, such as vinyl esters of carboxylic acids, for example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate; esters of unsaturated acids, for example, methyl acrylate, ethyl acrylate, butyl acrylate, allyl acrylate and the corresponding esters of methacrylicacid; vinyl aromatic compounds, for example, styrene, orthochlorostyrene, parachlorostyrene, 2,5-dichlorostyrene, 2,4-dichlorostyrene, paraethyl styrene, divinyl benzene, vinyl naphthalene, alpha-methyl styrene; dienes, such as butadiene, chloroprene; amides,

of maleic, crotonie, itaconic, fumaric acids the in e understood s l mitiasl'fliq @992? f. th invasio as i it is realized a c g s h r thia are p ssib e as? it is fux ther intended that each element recited in any or the following claims is tube understood as referring to all new equivalent elements for accomplishing substantially the a same results in substantially the same or equivalent Inanner, itbeing intended to cover the invention broadly in whatever form its principle may be utilized;

What is claimed'is: n g f l. A process for producinga high quality polymer which comprises intimately mixing in water an, ethyleni cally unsaturated monomercontain'ing at least about "@571? vinyl halide and a dispersing agent cbnsistinge ssentially of gelatin in an amount frbm'about 9. 1 to oksagm gi weight of monomer, the resulting solution having a at least as highfas the isoelectric pl-I of the gelatin; thin-1 oughly agitating this aqueous polymerization medium to, form a stable dispersion of monomer in watergthgreatter halide s vinyl ch 'qr st adding an acid to lower; of: the aqueous polymerization medium to a value within the range from 2 to 5, inclusive, "below the isoelectric pH of the gelatin, and nolymss zlns sa mnncmc in, e mu -formed u pe sion u a a v y l 2. The process according to claim 1 wherein said vinylproce s ac o d o cla m 1 w tc aid. vi hlQn-idm a 4. The process according to claim 1 wherein the agi; tation of the monomer-water dispersing agent mixture is csniisuqq tq ab ut 5 m autcs s 2 10 1;; h ess s ci siasl t t t P 9 acc rd ng 9 a m wherein he as?! ahq lxi sasid.

he a c s accus n #9 la m. 1 h tqin a PQEQEY BQWPJQIFFQQI! ca a t saddsd o thi aqu u P9!!!- References Cited in the file of this gate'nt N TED S AIESP I NIS U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION I Patent No. 2,833,754 Roger G. Richards et al. May 6, 1958 It is hereby certified that error appears .in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 34, for generaly" read generally column '7, line 58, for "160 F," read 160 F, column 8, line 17, for "prefenred" read preferred column 10, line 24, for "expoxidized" read epoxidized line 42, for "produce" read reduce line '74, for "exmple" read example Signed and sealed this 24th day of June 1958.

(SEAL) Attest:

KARL H, AKLINE ROBERT C.\ YIATSON Attesting Officer Carmissioner ofPatents 

1. A PROCESS FOR PRODUCING A HIGH QUALITY POLYMER WHICH COMPRISES INTIMATELY MIXING IN WATER AN ETHYLENICALLY UNSATURATED MONOMER CONTAINING AT LEAST ABOUT 85% VINYL HALIDE AND A DISPERSING AGENT CONSISTING ESSENTIALLY OF GELATIN IN AN AMOUNT FROM ABOUT 0.1 TO 0.45% BY WEIGHT OF MONOMER, THE RESULTING SOLUTION HAVING A PH AT LEAST AS HIGH AS THE ISOELECTRIC PH OF THE GELATIN, THOROUGHLY AGITATING THIS AQUEOUS POLYMERIZATION MEDIUM TO FORM A STABLE DISPERSION OF MONOMER IN WATER, THEREAFTER ADDING AN ACID TO LOWER THE PH OF THE AQUEOUS POLYMERIZATION MEDIUM TO A VALUE WITHIN THE RANGE FROM 2 TO 5, INCLUSIVE, BELOW THE ISOELECTRIC PH OF THE GELATIN, AND POLYMERIZING SAID MONOMER IN THE THUS-FORMED SUSPENSION. 